On Sun, May 12, 2024 at 04:17:06PM +0200, Erick Archer wrote:
> This is an effort to get rid of all multiplications from allocation
> functions in order to prevent integer overflows [1][2].
>
> As the "dl" variable is a pointer to "struct hci_dev_list_req" and this
> structure ends in a flexible array:
>
> struct hci_dev_list_req {
> [...]
> struct hci_dev_req dev_req[]; /* hci_dev_req structures */
> };
>
> the preferred way in the kernel is to use the struct_size() helper to
> do the arithmetic instead of the calculation "size + count * size" in
> the kzalloc() and copy_to_user() functions.
>
> At the same time, prepare for the coming implementation by GCC and Clang
> of the __counted_by attribute. Flexible array members annotated with
> __counted_by can have their accesses bounds-checked at run-time via
> CONFIG_UBSAN_BOUNDS (for array indexing) and CONFIG_FORTIFY_SOURCE (for
> strcpy/memcpy-family functions).
>
> In this case, it is important to note that the logic needs a little
> refactoring to ensure that the "dev_num" member is initialized before
> the first access to the flex array. Specifically, add the assignment
> before the list_for_each_entry() loop.
>
> Also remove the "size" variable as it is no longer needed and refactor
> the list_for_each_entry() loop to use dr[n] instead of (dr + n).
>
> This way, the code is more readable, idiomatic and safer.
>
> This code was detected with the help of Coccinelle, and audited and
> modified manually.
>
> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#open-coded-arithmetic-in-allocator-arguments [1]
> Link: https://github.com/KSPP/linux/issues/160 [2]
>
> Signed-off-by: Erick Archer <erick.archer@xxxxxxxxxxx>
Looks right to me. Thanks!
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
--
Kees Cook
